This invention relates to multi-dimensional ultrasound imaging. In particular, methods and systems for free-hand or user operated scanning for three-dimensional (3D) ultrasound imaging are provided.
For 3D ultrasound imaging, a one-dimensional linear array transducer may be used to acquire a plurality of two-dimensional frames of data or images. A three-dimensional volume is scanned by obtaining a plurality of two-dimensional images in different planes. For example, the transducer is held in one location and rotated about an azimuthal axis to scan part of a cylindrical volume. Another example is translating the transducer along an elevation dimension or perpendicular to the array of elements over the surface of the skin. Knowing the relative positions of each scan plane to other scan planes results in more accurate three-dimensional imaging. However, one-dimensional linear arrays provide limited information of scan plane position relative to other scan planes, leading to uncertainty and poor quality three-dimensional representations.
Various methods and devices have been developed for determining the relative position of scan planes. The decorrelation of ultrasound data from one scan plane relative to ultrasound data of an adjacent scan plane may indicate a distance between scan planes, such as disclosed in U.S. Pat. No. 5,876,342, the disclosure of which is incorporated herein by reference. A mechanical structure to mount the transducer may be used to accurately measure or position the transducer for scanning each of spaced scan planes, but such brackets or mountings are difficult, time consuming and cumbersome. Magnetic position sensors or gyroscopes within the transducer provide signals indicating the movement and orientation of the transducer for determining the position of scan planes. These types of sensors may add undesirable weight and complexity to the transducer and metallic objects in the examination area may adversely affect the performance of magnetic position sensors. Cameras, infrared sensors or other sensor positioned within a room for ultrasound scanning remotely identify the position of the transducer on the patient or LEDs on the transducer on the patient, but obstructions may interfere with these devices.